AQA C3 Chemistry

Every 8th element had similar properties (octaves), it was arranged by atomic mass and there were 2 elements in the same box.

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How did Mendeleev arrange the periodic table?

Arranged by atomic mass, had similar properties and left gaps for elements yet to be discovered.

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How is the modern periodic table arranged?

Metals and non-metals, arranged by proton number, it has groups - number of electrons of outer shell and periods - number of shells.

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What are Group 1 - Alkali metals?

They have 1+ ions, the universal indicator is purple, their reactivity increases down the group, they have less electrostatic force and it is easier to lose due to shielding effect of other electrons.

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What are Group 7 - Halogens?

They have 1- ions, coloured vapours, diatomic molecules, they form ionic compounds with group 1, reactivity decreases down the group, it is harder to gain an electron due to shielding effect of other electrons and there is less electrostatic force.

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What is Halogen displacement?

A more reactive halogen will displace a less reactive one from a compound.

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What are the properties of transition metals?

Compared to group 1, they have a higher melting point, they are stronger/harder, they are much less reactive and they have a higher density.

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Transition metals are...

Used for catalysts, form coloured compounds, ions with different charges and they usually have the same number of electrons in the outer shell.

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What is Scum?

What is formed when hard water reacts with soap.

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What is Scale?

What is formed when hard water is heated. It is basically limescale which is Calcium Carbonate, which is a solid and forms on metal appliances reducing efficiency.

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How can you remove hard water with washing soda?

Add Sodium Carbonate to the water. This precipitates out the Ca and Mg ions to form insoluble Carbonates.

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How can you remove hard water through an ion-exchange column?

The ion-exchange column is filled with resin containing Sodium and Hydrogen ions. As the water is passed through the resin, the Na and H ions EXCHANGED with the Ca / Mg ions. This needs to be topped up with Na ions so NaCl is poured in to replenish.

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What is titration used for?

It is used to determine accurately how much alkali is needed to react completely with a known volume of acid (or vice versa).

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What is Phenolphthalein?

A strong alkali and weak acid.

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What is Methyl Orange?

A strong acid and weak alkali.

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How do you carry out a Titration calculation?

First convert the volume into dm^3 by dividing by 1000. Then calculate the moles of the substance of the known volume and concentration. Next look at the equation for the ratio. Finally re-arrange the formula to allow you to work out the unknown.

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What does exothermic mean?

When heat is given OUT.

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What does endothermic mean?

When heat is taken IN.

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What does a catalyst do?

Speeds up a reaction.

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What colour does the flame go when Barium is used to test for positive ions?